EU Brexit negotiator Michel Barnier said Tuesday that Brexit talks had not made enough progress to unlock the next phase as MEPs prepared to vote on a motion criticising Britain.

Addressing the European Parliament in Strasbourg, Barnier said ‘serious differences’ remained on Britain's divorce bill, the rights of EU citizens living in Britain, and the fate of Northern Ireland.

MEPs, meanwhile, took the opportunity to put the boot into British Prime Minister Theresa May's Conservative party, which is holding its annual conference, over its deep divisions on Brexit.

‘Today we have not yet achieved sufficient progress to begin in full confidence the second phase of negotiations,’ Barnier, a former French minister and European Commissioner, told MEPs.

‘There are still serious divergences, in particular on the financial settlement. We will not agree to pay at 27 what was decided at 28,’ he said, referring to the remaining 27 EU member states.

EU leaders are to decide at a summit starting on October 19 whether enough has been agreed on the divorce to start discussing the future relationship including a trade deal, as Britain has demanded.

But the European Parliament, which will have a final veto on any deal for Britain's departure from the bloc in March 2019, will vote Tuesday on a resolution calling on EU leaders to postpone the decision.

The move comes despite a speech by May in Florence last month offering concessions, which Barnier told MEPs had been ‘translated into negotiating positions’ by her negotiating team led by Brexit minister David Davis.

- 'Sack Boris Johnson' -

European Commission President Jean-Claude Juncker also said it was too soon to move on to the next phase.

‘We first need to agree on the terms of the divorce and then we see if we can half-lovingly find each other again,’ Juncker told parliament.

Juncker also warned Britain not to try and ‘go over Michel Barnier's head’ and negotiate directly with European leaders, saying he was the only one mandated to carry out Brexit talks.

The MEPs' resolution, backed by all the major political groups, is harsh on Britain's refusal so far to settle the exit bill, saying that the ‘absence of any clear proposals has seriously impeded the negotiations.’

It says they are ‘of the opinion that in the fourth round of negotiations sufficient progress has not yet been made’ in the three key areas.

It also ‘calls on the European Council (of national leaders), unless there is a major breakthrough in line with this resolution in all three areas during the fifth negotiation round, to decide at its October meeting to postpone its assessment on whether sufficient progress has been made.’

The Brexit debate allowed top MEPs to take aim at May and her divided cabinet, particularly Davis and Foreign Secretary Boris Johnson.

‘Who should I call in London -- Theresa May, Boris Johnson or David Davis?’ said Manfred Weber, the head of the parliament's biggest group, the centre-right European People's Party.

Manfred even urged May to ‘sack Boris Johnson’, who has undermined May on a series of key Brexit issues and is due to speak at the Conservative party conference in Manchester on Tuesday.

British eurosceptic leader Nigel Farage -- who still holds a seat in the European Parliament -- meanwhile said May was a ‘waste of space’ and should resign.

The fifth round of Brexit talks is due to start in Brussels on Monday.